Rotational spectra of isotopic species of methyl cyanide, CH3CN, in their v8 = 1 excited vibrational states

摘要

Context. Methyl cyanide is an important trace molecule in space, especially in star-forming regions where it is one of the more common molecules used to derive kinetic temperatures. Aims. We want to obtain accurate spectroscopic parameters of minor isotopologs of methyl cyanide in their lowest excited ν8 = 1 vibrational states to support astronomical observations, in particular, with interferometers such as ALMA. Methods. The laboratory rotational spectrum of methyl cyanide in natural isotopic composition has been recorded from the millimeter to the terahertz regions. Results. Transitions with good signal-to-noise ratios could be identified for the three isotopic species CH313CN, 13CH3CN, and CH3C15N up to about 1.2 THz (J′′ ≤ 66). Accurate spectroscopic parameters were obtained for all three species. Conclusions. The present data were already instrumental in identifying ν8 = 1 lines of methyl cyanide with one 13C in IRAM 30 m and ALMA data toward Sagittarius B2(N).